In a heat-transfer recording apparatus, recording of image information is carried out by putting a heat recording medium (hereinafter, referred to as ink donor sheet) on a recording paper.
FIG. 1 shows a sectional structure of a conventional ink donor sheet. In the ink donor sheet 10, a heat-transfer (heat liquifying or heat-subliming) ink layer 12 is formed on a side of a thin paper base 11 having a thinkness of about 50 .mu.m so as to have a thickness of about 10 .mu.m. When a recording paper is brought into contact with the ink layer 12 and a heat pulse is applied from the side of the paper base 11, the ink on the heated part of the ink layer 12 liquifies or sublimes and is transferred to the recording paper, by which the image information is recorded.
A certain degree of heat resistance is required for the paper base of the ink donor sheet. Further, it is important to avoid interior transfer caused by sticking when the donor sheet is brought into contact with a thermal head for applying a heat pulse. For such a reason, condenser paper has been principally used until now as the paper base. However, papers composed chiefly of vegetable fibers such as condenser paper, etc. are easily influenced by moisture, which can cause expansion and contraction. As the result, for example, in an apparatus wherein heat-transfer recording is carried out by supplying a long ink donor sheet from a supplying roll to a thermal head of the recording part, waves are sometimes formed on the surface of the thin sheet, if the ink donor sheet is moistened at it moves toward the supplying passage. If ink donor sheet on which waves are formed becomes creased on the recording part it will cause the occurrence of inferior transfer.